Mounting arm for sound translating device



July 15, 1952 BAKER 2,603,490

MOUNTING ARM FOR SOUND TRANSLATING DEVICE Filed April 11, 1945 2 SHEETSSHEET 1 SJ DO A D J. BAKER July 15, 1952 D. J. BAKER MOUNTING ARM FOR SOUND TRANSLATING DEVICE 2 SHEETS.-SHEET 2 Filed April 11, 1945 9:30AM Ada E.mm Amizmwzmk womb n m km 2TH no ZoEQmonm Q H Ho E 8 zozumom Patented July 15, 1952 Donald J. Baker, Los Angeles, Calif.

Application April 11, 1945, Serial No. 587,757 a This invention relates to a mounting arm of the type commonly referredto as a pickuparm or a tone arm for supporting a pickup head or other sound translating device inoperative relation with a disk-type of sound record. While my mounting arm is especially suitable for supporting the pickup head of a sound reproducmachinaiit'will'be obvious that the arm may be used for supporting ,a sound recorder or a sound-box or other.;sound translating device.

The mai'ri'object 'ofthe' invention is to'devise a mounting arm for. a sound translating device cooperatingwith a disk-type of record'such that the fore and-aft axis :of the sound translating device remains substantially tangent to the sound groove on therecord at the point where the stylus or heedleren'gages the record. Stated more accurately, the vertical plane Which includes the iore-andaft axis of the sound translating device remains tangent to the groo e at the point where the" needle engages the record. The many advantages .which accrue irom maintaining a tangenturelation of the sound.

translating device; withrespect to the record groove have been stated very completely in a number of articles :in the published literature dealing with the subiect,iand these advantages neednotberepeatedfhere. Y Various arrangements have been proposed for securing an approximation of the tangent con-v dition. 'SolileOf these arrangements are quite complicatedand impractical while: others havev gone into extensive "use. One arrangement commonly usedinvolvesqa-rigid tone arm pivoted on a vertical axis near the edge of the turntable and having the sound translating device mounted so that when/the arm is -moved to the center-of the record the needle-'01 stylus overhangsthe recordcentering pinQby aKGBI'EtEin amount, and the axis of the translating device, is arranged at an angle to the-line passing .through the, point of the needle and through, the-pivotal axis of the tone arm. This arrangement-does not secure a tangent relation for. a11=posit1ons of the stylus on the'record; but-'the axisofthe translating device varies from the tangent'relation according to the radial distance from the center of the record tothe needleor stylus. This has been shown in an article by B: BaBauerappearing in Electronics for March;-.1 94.5.' ;-.A So, such arrange ments-do not eliminate said groove wear,

In case of a rigid tone arm swinging about a fixed vertical axis, the amount of mistrackin could be reduced materially bythe use of a long arm, but limitations on space and weightof the j v Claims. (01. 2744s) armvma'ke it necessary to-use a relatively short arm where thefixed pivotal axis. is-located near the edge of the turntable. v

, My invention employs'a rigid tone arm, but

Y instead of mounting the arm to swing about a fixed pivital axis, the arm is mounted to swing about a vertical axis which also moves along a predetermined path during the swinging ofthe arm. The amount of movement of the pivotal axis of the arm along the path is controlled by a link which is pivoted at one end on a fixed vertical axis and has a pivotal connection with the tone arm at a point between-its pivotal axis and the free end of the arm. The sound translating device is mounted on the end of the tone arm with its fore-and-aft axis inclined to the line passing through the point of the needle and the pivotal axis of the arm. a

One embodiment of myv invention is illustrated in the accompanying drawings inwhich Figure 1 is a plan view showing'the tone arm mounted for cooperation with a record on a turntable;

Figure 2 is an elevational view ofFigure 1 with the rear end of the arm shown insection to illustrate the arrangement of the supporting structure; r

Figure 3 is a sectional View of Figure 2 taken along-the plane 3- 3 c Figure 4 is a side elevational view of Figure 1;

Figure 5 is an end view of the tonearm as shown in Figure 4; and

Figure 6 is a diagram illustrating the Operation of the invention. I

Referring to the drawing, a turntable '1 car.- ries a. disk record 2 which is centered onthe table by centering pin 3, the turntable being supported. by a suitable plate or board 4. The tone arm 5 is formed of a rigid member, preferably a hollow member having it crossesection of inverted U-shapes At the free end of the tone arm-is mounted a pickup 6 or other sound translating device having its-fore-and-aft axis 6a inclined to the axis of the arm 5 in the manner block 8 is-pivotally SUPDQIted'on a hOriZOntal axis 10. Alinkjd is arl'an'ged beneath tone arm 5 zontal axis Ic with block 8 when the arm is raised r from the record. I

The lower portion of the arm at the rear end of the arm is cut away as shown in Figure 4 to permit the rear end of the arm to clear the upper face of the block 8. This block is provided i V with a horizontal tail piece 80 arranged under the extreme rear end of the arm 5 as shown in Figure 2 and which also extends to one side of the rear endof the arm as shown in Figure 1. This. tail pieceiisproyided with a slot Bc'which receives a guiding pin 5a which is mounted near the rear end of v.the'arm 5 and extends into the slot 80. Y As will be seen from Figure 1, the guiding slot 8c' .has a straight portion which is in alignment with the axis. of the arm 5 when in the position shown in solid lines in Figure 1. This straight portion of the slot is at right angles to the pivotal axis. Ic of the block 8. The rear portion of, the slot 80' turns and goes off at an angle to one side of the axis of arm 5 as shown in Figure 1 and the purposeof this construction will be explained later. Block 8' is also provided with a vertical tail piece 8d .at. the rear end thereof which forms a support for a counterweight 8e which may be adjusted towards or away from the pivotal axis 10. I v A vertical bracket or standard I! is mounted to one side. of. the turntable I and serves to support the tone arm 5 during changing of the record.

Connections to the pickup 6 are made byconductors I2 which pass from the pickup 6 back through the hollow arm 5 on opposite sides of the bracket l0 and then enter a cavity 8f formed in the upper face of block 8 and then pass downwardly through a vertical hole formed in block 8, and then through aligned vertical holes formed in the base of bracket 1 and supporting plate 4. The provision of a loop ,l2a in the conductors I2 within the cavity 8f avoids any undue interference with the movement of the tone arm. Y

The location of the mounting bracket I is determined in the following manner. The horizontal and vertical axes of the record are established at right angles to each other as shown at IA and 113 in Figure 1. The longitudinal axis IA of bracket I will be parallel with axis IA as shown in Figure 1, and the distance 1B between this axis and the axis IA. is determined in the following manner Assume that the angle 6a between the axis (in of the heads 6 and the axis 5A of thearm 5 is to be 22; then a radial line I3 is drawn through the center of the record at an angle of 22 to the left of the lower part of the axis IB. The outer boundary of the recording on the recordis represented by the circle 2a while the inner boundary is shown by the circleZb. The radial line I3 crosses these two circles atthe points I311; and i312, respectively. A point C is located midway between the points Ba and 13b, and the bracket axis IA is drawn through this point parallel with axis IA. For a twelve-inch record, the distance IE will be 4 portion of the record is three inches and the outer diameter of the recording is twelve inches.

The point C indicates the point of engagement of the needle with the record when the tone arm is in the position shown in solid lines in Figure l where the axis 5A of the arm 5' is coincident with the bracket axis IA, and the axis 6a of the head Bis tangent to the groove at this point, since the angle l3d between'the line I3 and axis lB is equal": to the angle 6a. i

The distance 53 from the point of the needle 6b back to the pin 5a may be selected at any Q convenient distance depending upon the space available. Assume this distance to be ten inches then the point 5a. on the axes 5A and IA will be located ten inches from the point C and the axis' 5a of pin 5awill remain at this constant distance from the needle 6b for all positions of the arm 5.

in the neighborhood of three andone-half inches,

Furthermore, the axis 5a is to remain on the axis IA for all operative positions of the arm. In order to maintain the tangent'relation of the. pickup head, it will'be necessary' 'to shift the axis 5a along the axis IA as the arm 5 moves across the record. The pin 50, is constrained to travel along the axis IA by a portion of the groove which is formed coincident with the' axis IA.

It will be understood that in order to maintain the tangent relation of head 6 with respect to'the groove, the radial line passing through the center of the record and the point of the needle must'bear a constant angular relation to the axis 5A of the arm 5. This constant angle is indicated by the'angle I3e in Figure 1. The point D at which the path of travel of the needle en'- ters the blank portion of the record is determined by drawing a radial line l3 which intersects the circle 2 b at point D and the angular position at line I3 is such that the distance between the point D and the point 'at which the arm axis 5A intersects the axis IA'is equal to the distance'5B, and in the example assumed, this would be ten inches. It will be found that the point D is so located that the pin 50. has moved-to the right so that its axis now occupies the position shown at 5a" in Figured." 1

-In a similar manner, the point B at which the needle crosses the circle 2a representing the outer boundary of the recording i'slocated by establishing a radial line [3": 'a'tan'angular'position such thatfthearm axis 5A" intersects the axis IA at thepoint 5a".- This is clearly shown in Figure'fi. 1 A dotted arc E is now drawn about the point 5a passing through the points 3 and D. In Figure 6 the dot-dash curved line T indicates the path 'of trav'elof the needle for the true tangent relation, and the distance between the point C and the pointEa at'which the curve E intersects the axis 5A determines the maximum amount of shift of the axis of pin 5a along the axis IA as the tone arm travels across the record. In other words, thedistance' between thepoints c and Ellis equal to the distance between the points 5a and 5a"'in Figure 6.

In Figure 6 the points 9a and 9?) indicate the locations of the axes of the pivot pins 9a and 9b,

respectively, on link {I when the arm axis 5A is coincident with the bracket axis IA. The axis 9a remains fixed, while theaxis 9b'swings' about the axis 8a. The effective length'of link 9, or the spacing between the axes of pivot pins 9c and 9b, is. determined in the following manner. A

point 91) is placed onthe axis 5A,at a convenient location as shown by the distance 9A in Figure ,6. Similar points 91)" and 919"" are placedon the lines 5A and 5A" at the same distance 9A from the point $5077. A circle is now drawn through the three points: 9b.'.,' 912". :an'diQb' with the center oixthe circle located :at Sat m1 the axis "LA. The" radius of "this "circle will berthe-ieffeoe itive length \of link/9 'andrequal to th'e'rdistance -9B-in:F.'igurel. r v.

Fromthe foregoing-it willbe :seenithait'a aperfect'tan'gent relation .of: the npickup head 'is ob,- tained v:at at .least three different positions of the head corresponding to the points B-,'*=C and D, on the curve T. This marks a distinct improvement over prior arrangements using rigid tone arms where the paths of travel of the needle intersects the true tangent path at only two points. While the pickup head may depart from'th true tangent relation to a small degree between the three points mentioned, the amount of; deviation is very small and has no noticeable effect on the operation. 7

If the mounting arm were pivoted at the point 5a", the: path of movement of-the needle would be along the dotted line E in Figure 6, and the pickup head would have a'-'true tangent relation only at the points B andID where the curve '13 intersects thecurveC, The greatest deviation from the tangent relation would be found at the middle of the grooved portion of the record, and this deviation would be indicated by the angle between the radial lines passing through the points C and Ea which in the example shown would bebetween 4 and 5. According to'my invention the angle of deviation is reducedjto zero at the point C, and it is negligible for all other points in the path of travel'of the needle.

Since the link 9 is of limited length,it would limit the amount of movement of the mounting arm away from the center of the record, and in order to allow the arm to be moved entirely clear of the record and turntable, for the purpose of changing records, I form the rear portion of the slot 80' at an angleto the axis 1A. -In Figure 1 the rear portion of the slot turns back at an angle greater than 90", but this angle is not at all critical and it may be a right angle as shown in Figure 6. When the pin 5a enters the laterally extending portion of the slot, the arm 5 is allowed to pivot about the pivot pin 91) of the link 9, and this permits free movement of the arm beyond the edge of the turntable and into a position where it may rest upon the standard I I, as shown in the dotted line position in Figure 1. It will be understood that the pin 5a does not enter the laterally projecting portion of the slot until the needle has moved beyond theouter boundary of the curved portion of the record.

In Figure 6 the pin 5a occupies the position shown at 5a when the armis moved to the position A.

From the foregoing it will be understood that my invention provides a mounting arm which is pivoted near one end so the arm will swing through a predetermined arc, and movement of.

the arm causes the pivotal axis of the arm to shift in a direction transversely of the are through which the needle swings, or substantially parallel with the mid position of the line passing through the needle point and th pivotal axis of pin 5a.

By eliminating the over-hang in the stylus mounting and by maintaining the tangent rela-- tion throughout the path of travel of the stylus, my invention entirely eliminates the side groove wear which is present in prior devices.

It may be noted that the path of travel of the stylus over the grooved portion of the record and represented by the dot-dash line T in Figure 6 through the center or-the record. 1

In describing my invention .1 ihaveggiven one example forfiusewith 7 a twelve-inch recordbut the principles: of my inventi n'=may ::b applied to records or other diameters. For largertrecords, such as a seventeen inch record; the tone arm will be longer and theilinks willials "be longer than for a twelve-inch record ii a claim: x v .-f 1; An arrangement for; mounting "a sound translating device comprising, :in combination, .a mounting block, means ,for mounting said block for movement about a .fixed horizontal -axis, a tone 'armarrangedtransversely oisaid horizontal :axis,--;means vfor connecting said arm for pivotal movement with said block about said horizontal :axis comprising a link element .pivotally connected at one end to'sai'd' block Ion a vertical axis and pivotally connected'atthe-other end to-said arm on a second verticaraxis and at a point intermediate the ends of saidar-m, one end of said arm'havi'ng saidtransla'ting device mounted thereon and the other end being located adjacentsaid block, and pivotal means interconnecting said other end ofsaid arm and said block for constraining the horizontal "movement of said arm about a vertical axis located adjacent said other end of said arm, saidfpivotal' means being free to move along a -path transverselyoi' said horizontal axis; I I

2. An arrangementacoording=to claim 1 where in saidpivotal means comprises a {pin element carried by the rear end of said arm and having the end thereof positioned within a guiding slot formed in said mounting block substantially at right angles to said horizontal axis.

3. An arrangement for mounting a sound translating device for cooperation with a disktype sound record comprising in combination, an arm having a longitudinal axis, means fixedly supporting said translating device in the free end of said arm so that there is an angle of constant value between the vertical planes passing through the longitudinal axis and the fore-andaft axis of the sound translating device, respectively, pivot means near'the other end of said arm providing a vertical pivotal axis about which I the longitudinal axis of the said arm when the free end ofsaid arm is in mid position radially of the grooved portion of the record, and means controlled by the swinging of said arm about said vertical pivotal axis for shifting said pivot means along said linear path.

4. A mounting arrangement for a sound translating device comprising, in combination, an arm having a sound translating device fixed to the free end thereof, a stationary support, pivot means near the other end of said arm cooperating with said stationary support to mount said arm for movement about a vertical pivotal axis as said sound translating device traverses the grooved portion of a disk-type sound record, said pivotal means being constructed to permit move.- ment of the vertical pivotal axis of said arm along a linear path which is substantially parallel to the longitudinal axis of the said arm when the free end of said arm is in mid position transversely of the grooved portion of the record, and means controlled by movement of said arm when it is atleither side of said mid position for provided on the other end of said arm for holding said 'arm .on said support for directed movement about a vertical axisbetween two end positions forming an angle with respect to one another, said pivotal means being shiftable with respect to said support along a linear path substantially parallel with the longitudinal axis of said arm when the free endof said arm is in mid position between said'two end positions, and means controlled by the horizontal movement of said arm about saidvertical axis on either side ofsaid mid position for shifting said pivotal means along said linear path in a, direction away from the free end of saidarm.

6. A mounting arrangement according to claim wherein said last recited means comprises a link element having one end thereof pivoted on a fixed vertical axis, and means for pivotally connecting the free end of said link to said arm at a point intermediate the free end thereof and said pivotal means providing a vertical axis for said arm.

,7. An arrangement for mounting a sound translating devicevfor cooperation with a disktype sound record comprising, in combination, anarm having said translating device fixed at the free end thereof, pivot means secured to said arm at a fixed distance from said translating device for mounting said arm for swinging move- .ment over the grooved portion' 7 or said record,

said pivot means-being arranged-for movement along a linear 'pathisubstantially' parallel to the longitudinal axis of thear'm when the free end ofthe arm is in mid position radially of the grooved portion of the record and-means connected to said arm'at a point between said translating device and'said pivot means for constrain- REFERENCES CITED The following references are of record in the file of this patent: J V

' UNITED STATES PATENTS Number Name Date 1,885,994 Dieux Nov. 1, .1932 1,963,673 Patino June.19, 1934 2,006,605 Putnoky July 2, 1935 2,025,300 Mueller Dec. 24, 1935 2,192,464 Yasuda et a1 Mar. 5, 1940 2,303,619 Davis Dec. 1, 1942 FOREIGN PATENTS Number l Country Date 1 116,163 Great Britain June 6, 1918 289,984 Great Britain May 10,1928 676,429 France Nov. 28, 1929 372,317 GreatBritain Apr. 29,1932 558,504 Germany Sept. 8, 1932 386,851

Great Britain- Jan. 26, 1933 

